1. Field of the Invention
The present invention relates to a circularly polarized antenna that receives a circularly-polarized microwave transmitted thereto, and rectifies the received microwave so as to produce electric power, and a rectenna using the circularly polarized antenna.
2. Description of Related Art
For example, Japanese patent application publication No. 5-110,334 discloses the structure of a prior art circularly polarized antenna element. The antenna disclosed by this patent application publication is provided with a ground conductor disposed on a back surface of a dielectric board, a ring patch antenna having perturbation elements on a surface thereof, and a power feeding conductor pattern that is so placed as not to be in contact with the ring patch antenna, and is so constructed as to supply electric power to the power feeding conductor pattern from the back side of the dielectric board. The prior art antenna element can form a radiation field by means of the ring patch antenna and the ground conductor by supplying electric power to the power feeding conductor pattern, and can create circularly-polarized-wave radiation by virtue of the operations of the perturbation elements.
[Patent reference 1] Japanese patent application publication No. 5-110,334.
In the antenna element disclosed in Japanese patent application publication No. 5-110,334, it is necessary to make sure that the dielectric board has a certain thickness or more in order to maintain the characteristics of the radiation field formed by the ring patch and the ground conductor. Japanese patent application publication No. 5-110,334 discloses a case where the dielectric board has a thickness B=1.3 mm, as an example. A problem with the prior art antenna element is that it is difficult to make the thickness of the dielectric board thin because the prior art antenna element has a ground conductor. Another problem is that the thickness of the whole of the prior art antenna element increases because electric power must be supplied to the power feeding conductor pattern from the back side of the dielectric board.